1. Field of the Invention
This invention in general relates to a process for removing photoresist material and particularly relates to a process for removing photoresist material in the manufacture of a CMOS (Complementary Metal-Oxide Semiconductor) photosensor.
2. Description of the Related Art
Conventionally, a charge-coupled device is used in a digital sensor. However, due to the cost and the size of the charge-coupled device, the CMOS photosensor has been recently developed.
A CMOS photosensor is electrically connected with other devices or other CMOS photosensors. A cover layer is used to protect and isolate the photosensitive area in the substrate to prevent electrical contact from the contact pad thereon. In such a case, the cover layer comprises a color filter layer for filtering a certain wavelength of light and an acrylic material layer as a planarization layer or a protective layer for the color filter layer.
In a conventional semiconductor fabrication, silicon glass or silicon nitride lies under the photoresist material. While removing the photoresist material using a plasma enhanced method, if the plasma contains oxygen, the silicon glass or silicon nitride doesn't react with oxygen. However, since the properties of acrylic material are similar to those of the photoresist material, it is difficult to remove the photoresist material by plasma without damaging the acrylic material layer after formation of an opening on metal pad by photolithography. Therefore, it is suggested that the photoresist material be removed using a solvent.
The photoresist material easily remains when the plasma is not used because the nature of the photoresist material changes after the ion-bombardment of plasma in the etching process. The surface of the photoresist material is parched. Thus, the photoresist material cannot be sufficiently removed by solvent. For example, after the etching process for patterning a passivation layer of a CMOS photosensor, the CMOS photosensor is removed to an Asher etching machine. The parched photoresist material is removed by oxygen plasma in the Asher etching machine. The remaining photoresist material is removed using solvent.
However, the Asher etching machine cannot precisely control a stable etching rate while etching the parched photoresist material. Etching temperature is increased according to etching time so that the etching rate is increased. Over-etching thus happens easily and the acrylic material layer may be damaged. Therefore, it is difficult to control etching time. Because of photoresist material remaining or acrylic material layer damage, the cover layer cannot maintain a planar form. In such a case, the light transmitted through the photosensor is interrupted, and the photosensitivity of the photosensor is thus decreased. Therefore, the complete removal of photoresist material on the cover layer in manufacturing a CMOS photosensor is desired, especially in industry-scale production.